Indicators, Acids, and Alkalis Flashcards
What is an indicator?
An indicator is just something that changes colour depending on whether it’s in an acid or in an alkali.
What is litmus paper?
Litmus paper is quite a popular indicator, but it only tells us whether a liquid is an acid or an alkali - it does not say how strong it is. Acids turn litmus paper red and alkalis turn it blue.
What is universal indicator?
Universal indicator solution is a very useful mixture of dyes which gives the colours shown in a pH chart.
How can you make red cabbage indicator?
1) Stir some cut leaves of red cabbage in a beaker of boiling water to obtain a red solution.
2) Filter the solution to remove all salts.
3) Add to acid or alkali.
It will turn pink/red if it is an acid, and it will turn green/yellow if it is an alkali.
What does the pH scale show?
The pH scale shows the strength of acids and alkalis. The pH scale goes from 0 to 14. pH can also be shown by colour universal indicator turns.
What is the pH of an acid?
Anything with a pH below 7 is an acid and will turn universal indicator red, orange or yellow.
What is the pH of the strongest acids?
The strongest acids have a pH of 0.
What is the pH of an alkali?
Anything with a pH above 7 is an alkali and will turn universal indicator blue or purple.
What is the pH of the strongest alkalis?
The strongest alkalis have a pH of 14.
What is the pH of a neutral substance?
A neutral substance (e.g. pure water) has a pH of 7 and will turn universal indicator green.
What do acids and alkalis do to each other?
Acids and Alkalis neutralise each other.
What is formed when acids react with alkalis?
Acids react with alkalis to form a neutral solution of a salt and water.
What is the word equation for neutralisation?
acid + alkali ==> salt + water
Why is it known as a neutralisation reaction?
This is known as a neutralisation reaction because the products have a neutral pH (a pH of 7).
What are everyday uses of neutralisation?
Treating indigestion or using toothpaste
What is the test and result for carbon dioxide?
Test: Bubble the gas through limewater
Result: Limewater turns milky/cloudy
What is the test and result for hydrogen?
Test: Place a lighted splint in a test tube containing the gas
Result: There will be a squeaky pop
What is the test and result for water?
Test: Transfer liquid into a sample of anhydrous copper (II) sulfate
Result: Anhydrous copper (II) sulfate turns blue
What is the test and result for oxygen?
Test: Place a glowing splint in a test tube containing the gas
Result: Glowing splint relights
What do most fossil fuels contain?
Most fossil fuels contain sulfur in compounds present as impurities.
What happens when fossil fuels are burnt?
When we burn the fuel, the sulfur is oxidised. It turns into sulfur dioxide (SO2) gas.
What do power stations give off?
Power stations burning coal or oil give off most sulfur dioxide; this is the main cause of acid rain.
What happens with sulfur dioxide?
It dissolves in rainwater and reacts with oxygen in the air, to form sulfuric acid.
What are some effects of acid rain?
- Trees are damaged and even killed
- Lakes in Norway and Sweden now have no fish in them
- Buildings and metal structures are attacked
